.TH ROUTE 8 "2014\-02\-17" "net\-tools" "Linux System Administrator's Manual"
.SH NAME
route \- show / manipulate the IP routing table
.SH SYNOPSIS
.B route
.RB [ \-CFvnNee ]
.RB [ \-A
family
.RB | \-4 | \-6 ] 
.TP
.B route 
.RB [ \-v ]
.RB [ \-A
family 
.RB | \-4 | \-6 ] 
.B add 
.RB [ \-net | \-host ] 
.I target 
.RB [ netmask 
.IR Nm ] 
.RB [ gw 
.IR Gw ] 
.RB [ metric 
.IR N ] 
.RB [ mss 
.IR M ] 
.RB [ window 
.IR W ] 
.RB [ irtt 
.IR I ]
.RB [ reject ]
.RB [ mod ]
.RB [ dyn ] 
.RB [ reinstate ] 
.RB [[ dev ] 
.IR If ]
.TP
.B route 
.RB [ \-v ] 
.RB [ \-A
.I family
.RB | \-4 | \-6 ]
.B del 
.RB [ \-net | \-host ] 
.I target 
.RB [ gw 
.IR Gw ] 
.RB [ netmask 
.IR Nm ] 
.RB [ metric 
.IR M ] 
.RB [[ dev ]
.IR If ]
.TP
.B route 
.RB [ \-V ] 
.RB [ \-\-version ]
.RB [ \-h ]
.RB [ \-\-help ]
.SH DESCRIPTION
.B Route
manipulates the kernel's IP routing tables.  Its primary use is to set
up static routes to specific hosts or networks via an interface after
it has been configured with the
.BR ifconfig (8)
program.

When the
.B add
or
.B del
options are used,
.B route
modifies the routing tables.  Without these options,
.B route
displays the current contents of the routing tables.

.SH OPTIONS
.TP
\fB\-A \fIfamily\fR
use the specified address family (eg `inet'). Use 
.B route \-\-help
for a full list. You can use 
.B \-6 
as an alias for 
.B \-\-inet6 
and 
.B \-4 
as an alias for 
.B \-A inet
.

.TP 
.B \-F
operate on the kernel's FIB (Forwarding Information Base) routing
table. 
This is the default.
.TP 
.B \-C
operate on the kernel's routing cache.
.TP
.B \-v
select verbose operation.
.TP
.B \-n
show numerical addresses instead of trying to determine symbolic host
names. This is useful if you are trying to determine why the route to your
nameserver has vanished.
.TP
.B \-e
use
.BR netstat (8)\-format
for displaying the routing table.
.B \-ee 
will generate a very long line with all parameters from the routing table.
.TP
.B del
delete a route.
.TP 
.B add 
add a new route.
.TP
.I target
the destination network or host. You can provide an addresses or symbolic 
network or host name. Optionally you can use \fB/\fIprefixlen\fR notation
instead of using the \fBnetmask\fR option.
.TP
.B \-net
the
.I target
is a network.
.TP
.B \-host
the
.I target 
is a host.
.TP
\fBnetmask \fINM\fR
when adding a network route, the netmask to be used.
.TP
\fBgw \fIGW\fR
route packets via a gateway.
.br
.B NOTE:
The specified gateway must be reachable first. This usually means that
you have to set up a static route to the gateway beforehand. If you specify
the address of one of your local interfaces, it will be used to decide about
the interface to which the packets should be routed to. This is a BSDism
compatibility hack.
.TP
\fBmetric \fIM\fR
set the metric field in the routing table (used by routing daemons) to \fIM\fR. If this option is not specified the metric for inet6 (IPv6) address family defaults to '1', for inet (IPv4) it defaults to '0'. You should always specify an explicit metric value to not rely on those defaults - they also differ from iproute2.
.TP 
\fBmss \fIM\fR
sets MTU (Maximum Transmission Unit) of the route to \fIM\fR bytes.
Note that the current implementation of the route command does not allow
the option to set the Maximum Segment Size (MSS).
.TP 
\fBwindow \fIW\fR
set the TCP window size for connections over this route to \fIW\fR
bytes. This is typically only used on AX.25 networks and with drivers
unable to handle back to back frames.
.TP
\fBirtt \fII\fR
set the initial round trip time (irtt) for TCP connections over this
route to \fII\fR milliseconds (1-12000). This is typically only used on
AX.25 networks. If omitted the RFC 1122 default of 300ms is used.
.TP
.B reject
install a blocking route, which will force a route lookup to fail.
This is for example used to mask out networks before using the default
route. This is NOT for firewalling.
.TP
.B mod, dyn, reinstate
install a dynamic or modified route. These flags are for diagnostic
purposes, and are generally only set by routing daemons.
.TP
\fBdev \fIIf\fR
force the route to be associated with the specified device, as the
kernel will otherwise try to determine the device on its own (by
checking already existing routes and device specifications, and where
the route is added to). In most normal networks you won't need this.

If \fBdev \fIIf\fR
is the last option on the command line, the word 
.B dev
may be omitted, as it's the default. Otherwise the order of the route
modifiers (\fBmetric netmask gw dev\fR) doesn't matter.

.SH EXAMPLES
.TP
.B route add \-net 127.0.0.0 netmask 255.0.0.0 metric 1024 dev lo
adds the normal loopback entry, using netmask 255.0.0.0 and associated with the 
"lo" device (assuming this device was previously set up correctly with
.BR ifconfig (8)). 

.TP 
.B route add \-net 192.56.76.0 netmask 255.255.255.0 metric 1024 dev eth0
adds a route to the local network 192.56.76.x via 
"eth0".  The word "dev" can be omitted here. 

.TP
.B route del default
deletes the current default route, which is labeled "default" or 0.0.0.0
in the destination field of the current routing table.

.TP
.B route del \-net 192.56.76.0 netmask 255.255.255.0
deletes the route. Since the Linux routing kernel uses classless
addressing, you pretty much always have to specify the netmask that is
same as as seen in 'route -n' listing.

.TP
.B route add default gw mango 
adds a default route (which will be used if no other route matches).
All packets using this route will be gatewayed through the address of a node
named "mango". The
device which will actually be used for that route depends on how we
can reach "mango" - "mango" must be on directly reachable route.

.TP
.B route add mango sl0
Adds the route to the host named "mango" via the SLIP interface (assuming that
"mango" is the SLIP host).

.TP
.B route add \-net 192.57.66.0 netmask 255.255.255.0 gw mango
This command adds the net "192.57.66.x" to be gatewayed through the former
route to the SLIP interface.

.TP
.B route add \-net 224.0.0.0 netmask 240.0.0.0 dev eth0
This is an obscure one documented so people know how to do it. This sets
all of the class D (multicast) IP routes to go via "eth0". This is the
correct normal configuration line with a multicasting kernel. 

.TP
.B route add \-net 10.0.0.0 netmask 255.0.0.0 metric 1024 reject
This installs a rejecting route for the private network "10.x.x.x."

.TP
.B route -6 add 2001:0002::/48 metric 1 dev eth0  
This adds a IPv6 route with the specified metric to be directly reachable via eth0.

.LP
.SH OUTPUT
The output of the kernel routing table is organized in the following columns
.TP
.B Destination     
The destination network or destination host.
.TP
.B Gateway
The gateway address or '*' if none set.
.TP
.B Genmask         
The netmask for the destination net; '255.255.255.255' for a host destination
and '0.0.0.0' for the 
.B default
route.
.TP
.B Flags 
Possible flags include
.br
.B U
(route is
.BR up )
.br
.B H
(target is a
.BR host )
.br
.B G
(use
.BR gateway )
.br
.B R
.RB ( reinstate
route for dynamic routing)
.br
.B D
.RB ( dynamically
installed by daemon or redirect)
.br
.B M
.RB ( modified
from routing daemon or redirect)
.br
.B A
(installed by
.BR addrconf )
.br
.B C
.RB ( cache
entry)
.br
.B !
.RB ( reject
route)
.TP
.B Metric 
The 'distance' to the target (usually counted in hops).
.TP
.B Ref    
Number of references to this route. (Not used in the Linux kernel.)
.TP
.B Use
Count of lookups for the route.  Depending on the use of \-F and \-C this will
be either route cache misses (\-F) or hits (\-C).
.TP
.B Iface
Interface to which packets for this route will be sent.
.TP
.B MSS 
Default maximum segment size for TCP connections over this route.
.TP
.B Window  
Default window size for TCP connections over this route.
.TP
.B irtt
Initial RTT (Round Trip Time). The kernel uses this to guess about the best
TCP protocol parameters without waiting on (possibly slow) answers.
.TP
.B HH (cached only)
The number of ARP entries and cached routes that refer to the hardware
header cache for the cached route. This will be \-1 if a hardware
address is not needed for the interface of the cached route (e.g. lo).
.TP
.B Arp (cached only)
Whether or not the hardware address for the cached route is up to date.
.LP
.SH FILES
.I /proc/net/ipv6_route
.br
.I /proc/net/route
.br
.I /proc/net/rt_cache
.LP
.SH "SEE ALSO"
.BR ethers (5),
.BR arp (8),
.BR rarp (8),
.BR route (8),
.BR ifconfig (8),
.BR netstat (8)
.LP
.SH HISTORY
.B Route
for Linux was originally written by Fred N.  van Kempen,
<waltje@uwalt.nl.mugnet.org> and then modified by Johannes Stille and
Linus Torvalds for pl15. Alan Cox added the mss and window options for
Linux 1.1.22. irtt support and merged with netstat from Bernd Eckenfels.
.SH AUTHOR
Currently maintained by Phil Blundell <Philip.Blundell@pobox.com> and Bernd Eckenfels <net-tools@lina.inka.de>.
